Background and Summary

This article provides an overview of an engine-monitoring system and other enhancements that will soon be available for new (by STC) and existing (by Form 337) Cirrus airplanes. The changes involve the addition of new hardware and software to the factory installed ARNAV ICDS 2000 Multi Function Display (MFD) system. N365DP, Cirrus SR20 line number 1062, has been used to test the installation and explore refinements to the displays. The airplane, owned by Delta Papa Ltd., is leased back to and based at Wings Aloft flying club in Seattle, WA at Boeing Field. Delmar Fadden and Peter Morton, retired Boeing engineers and principals of Delta Papa Ltd. worked with ARNAV on the evaluation and refinement of the engine monitor indications.

Wings Aloft has five Cirrus SR20’s available for rental now and a rapidly growing pool of SR20 pilots. N365DP gets plenty of exposure to pilots of varying familiarity with the Cirrus including members who are receiving initial instruction on the airplane.

In March of 2001, ARNAV installed a Data Acquisition Unit (DAU) Engine Monitor Computer for the ICDS 2000 in N365DP along with engineering software for the Engine Monitoring Display. Individual cylinder EGT and CHT sensors were added to the engine to support the new displays; the Cirrus installed EGT/CHT sensors and displays are unchanged. The airplane was operated over a month with this software load. In early May, an updated software load was installed and the outside air temperature sensor location modified as ARNAV approached the pre-production configuration for engine monitoring. This version of software includes engine-monitoring windows overlaying the map in addition to the full-page engine data display.

Engine Monitoring Experience

The first instance in which we experienced an economic/safety benefit from the Engine Monitoring Displays took place with the pre-production engineering software load on Friday May 11th. Our plan was to prepare N365DP for a flight to San Diego to support Sandel in the acquisition of the 3308 EHSI Supplemental Type Certificate. Wings Aloft had just completed the 300-hour check on the airplane. We were on our way to Puyallup to have the updated software installed by ARNAV. We expected to exercise the software thoroughly on the trip to San Diego the following week and give feedback to ARNAV so the system would provide maximum utility for Cirrus owners. During the pre-takeoff procedure at Boeing Field, we performed the magneto check with the full page engine monitor displayed on the MFD (Figure 1). We were surprised to see a 150-rpm drop and feel unusual roughness from the Continental engine on the right magneto. We repeated the mag check, and Del pointed to the #4 cylinder EGT display; it was rapidly decaying toward the bottom of the scale. We taxied back to Wings Aloft and reported our findings; sure enough the #4 cylinder bottom spark plug was fouled with a bit of oil soaked carbon and would not fire on the ground tester. Within 15 minutes the plug was cleaned and we were on our way; a major reduction over the time it would have taken to trouble shoot all six of the right mag spark plugs!

Figure 1. Full Page Engine Monitor Display

Arriving at Puyallup (all new comers to the Pacific Northwest have to pass a pronunciation test of that word before they are given a residence visa!), ARNAV gave us a thorough briefing and installed the pre-production software for the engine monitoring system. Del flew a test flight to explore the new features with the ARNAV staff, and we brought N365DP home for a good wash job in preparation for the San Diego Trip. ARNAV refers to the system as “EngineView”.

Flashback on Engine Monitoring Development

The previous two months had been devoted to intensive development by ARNAV to get the engine monitor system ready for production release. The purpose of the first trip to Puyallup in early March was to install the Data Acquisition Unit (DAU) engine monitor computer under the instrument panel on the co-pilot’s side, and install an additional outside air temperature sensor that would allow the computer to calculate a “% power” indication. The soft key text labels on the right side of the map screen (Figure 2) were changed to icons in preparation for the installation of the engine display control logic. The icons select, top to bottom respectively, Airports, Stormscope, Menus, Map scale +/-, Screen Brightness, Checklists, and MAP . The full-page engine parameters display (Figure 1), which is the “power up” mode of the system, received a thorough work out during the next several weeks of normal operation at Wings Aloft. The initial location of the air temperature sensor in the right engine inlet area was found to be unsatisfactory because it picked up too much engine heat. By the end of April, ARNAV and Cirrus had worked out a new temperature sensor installation on the right side of the fuselage opposite the production OAT sensor. The next software release included our first look at a % power indication and featured selectable windows for the engine data. The windows allow engine data to overlay a portion of the map on the left side of the display screen. Now we could see both map data and engine data on the same display, a great convenience in operating the engine and airplane. (Figures 4, 5, 6, 7 & 8) One week of operation with this installation raised questions about engine leaning and resulted in more detailed discussions with ARNAV. As initially configured the windowed EGT display on the MAP page did not have the sensitivity needed to perform engine leaning.  This meant having to switch to the full-page engine display to lean. While this would not be an excessive burden on the pilot, ARNAV wanted to do more to facilitate leaning, and set out to develop a method to allow leaning from the combined display.

Figure 2. MFD Icons

On Friday May 11^th, the pre production configuration was ready for installation and test. Our test flight with the ARNAV team showed that all features of the engine monitor were operational.  There were a few minor display artifacts and system noise that ARNAV wanted to refine and filter before the final production release, but none would interfere with our flight to San Diego.

Overview of New MFD Operation

At completion of the power up sequence after AVIONICS is turned on; the MFD shows the full-page engine display, see Figure 1 above. The pilot selects the FUEL page and specifies a full or partial initial fuel load for calculation of fuel remaining based on integrating fuel flow throughout the trip. The “ACK” (acknowledge) icon inputs the fuel load and the MFD reverts to the Figure 1 configuration.

Figure 3. Fuel Quantity Input Screen

Map Display Sequence

Selecting the lower right MAP icon (Figure 1) provides the first of three MAP displays (Figure 4), similar to the original delivered Cirrus configuration. The following series of photos in Figures 5 and 6 taken during the flight leg from Boeing Field to San Diego via Napa, CA show displays available by repeatedly selecting the MAP icon.

Map and Navigation Data Window

	The navigation data window has been moved to the lower left corner of the map display to maximize the available look-ahead map area and to provide room for the engine monitoring windows. A new data element to the right of the active waypoint caption in the navigation data window shows the calculated fuel necessary to reach the active waypoint.
Figure 4. MAP with Basic Navigation Data Window

Display Options: Full Compass Rose and Relocation of Obstacle Data Display

As shown in Figures 5 & 6, a new display option accessible from the MENU and Display Options selection provides a full compass rose around the airplane position when operating in track up orientation. We find this feature particularly useful for VFR operations in the vicinity of airports. Also, (see Figure 6) the Display Options selectable Obstacle Data display has been relocated under the airplane symbol to provide maximum area for navigation look ahead.

Basic Engine Data

	A second press of the map button adds the basic engine data window above the navigation data.
Figure 5. MAP with Basic Engine Data Window

The Basic Engine Data Window shows:

• PWR & OAT, % of power based on the new outside air temperature sensor and altitude.
• RPM, manifold pressure, oil pressure andtemperature, all use existing Cirrus sensors.
• Fuel panel indicates:
• FLW, Fuel flow, using original Cirrus fuel flow sensor.
• RMN, Fuel remaining = fuel used (Flow x Time) subtracted from initial set fuel load.
• DST, Fuel to destination based on current ground speed and fuel flow. Subtracting DST from RMN provides a continuously updated value of destination fuel aboard.
• MPG, Nautical ground miles per gallon; ground speed divided by fuel flow. A continuous indication of instantaneous flight efficiency.

Expanded Engine Data Window

A third press of the MAP button adds an EGT / CHT window above the basic engine data window. (See figures 7 & 8) Six green thermometer indications portray the EGT for each cylinder.  Six white bars show the corresponding CHT for each cylinder.  At the top of the window digital values show the highest of the six cylinder EGT and CHT values.  A blue box around the cylinder number at the bottom of the window indicates which cylinder is associated with the highest value.  The narrow bars projecting downward from the top of the window show the reduction in current EGT from peak EGT since reset on the Figure 1 display, and are an aid for use during leaning. The leaning procedure that uses these bars is described below.

Figure 6. MAP with Expanded EGT/CHT Window

Leaning The Engine to Best Economy and Best Power

Figure 7. Engine Monitor Windows Set for Best Economy	Figure 8. Engine Monitor Windows Set for Best Power

The engine monitoring system responds to any decrease in cylinder EGT by generating a narrow vertical bar that extends down from the top of the EGT display on the Engine Monitoring full-page display and also in the expanded EGT/CHT window of the combined display. Until the EGT reduction exceeds 50 degrees below peak, the bar is blue. Beyond that value the bar turns yellow. The first cylinder to peak causes the cylinder designation box to freeze and the digital value to follow that cylinder only.

Leaning Procedure

• Reset the LEAN function on the full page Engine Monitor display (Figure 1) to cancel any fluctuations in EGT that occur during takeoff and climb.
• Lean with reference to the Figure 1 page or the Figure 7&8 Expanded EGT / CHT window of the Map selection.
• Move the Mixture control toward Lean. The Engine Monitor checks the EGT value for each cylinder to determine when the peak for that cylinder is reached. After the peak temperature is reached, a small vertical bar above the related EGT begins to descend.
• For best economy, continue to lean and observe the vertical EGT bars. When the first cylinder reaches peak minus 50 degrees (see POH page 4-14) the related bar turns from blue to yellow. Move the Mixture control toward Rich until the bar returns to blue. Precision leaning for best economy is thus easy to achieve.
• For best power, lean the mixture until the first blue bar appears, and then richen the mixture until the first bar turns yellow. Richen an additional 25 degrees by reference to the digital display. We have suggested and ARNAV has agreed to add a tick mark at 75 degrees (see POH page 4-14) to the bar in order to facilitate this function.

Map Display Selection Summary

A fourth press of the MAP button selects the full-page engine data display shown in figure 1. In addition to the larger graphics this display provides a digital indication for each engine EGT and CHT display.

The next press of the MAP button starts the cycle again through the Map Navigation and Engine Monitoring Window series.

Stormscope Operation

When the optional Stormscope (WX-500) is installed the related icon incorporates a small square that appears as a red and white checkerboard if the Stormscope has detected a strike whether or not the Stormscope display is turned on. This is a particularly nice feature when operating at map ranges lower than the minimum Stormscope display range of 25 miles in the terminal area.

Engine Data Pop Up

The Engine Monitoring System will detect when any of the engine parameters are out of specified limits. If this occurs when operating in the Basic Map mode the MFD will switch to the full-page engine display giving the pilot the chance to make any needed decisions with all available data.  A selection on the engine display page allows the pilot to override this feature if automatic switching is not desired.

% Power Calculation

The Data Acquisition Unit (DAU) computer calculates % power based on an algorithm derived from the POH data and the temperature deviation from standard sensed by the new outside air temperature sensor. This calculation, when performed by the pilot using the POH, is a many step operation and, at best, yields approximate manifold pressure and rpm settings. Having the % Power available instantaneously during cruise, as well as during interrupted climbs and descents (especially under ATC control in IFR) is a great convenience and should result in more precise operation of the engine and greater opportunity to scan for outside traffic. We have suggested some minor changes to the % power window format, which ARNAV will incorporate in the production release. The POH charts and the algorithm that calculates the % power indication is based on the engine leaned for Best Power (see page 5-25 of the POH). Leaning does affect actual delivered horsepower, and we see that effect in the reduction in true airspeed at the lower fuel flow corresponding to Best Economy. Neither the POH nor the % power indication reflects the change in horsepower that occurs with mixture variation.

Data Recording

An electronic “snapshot” of all the data monitored by the Engine Monitoring System as well as the GPS data obtained from the Garmin 430 is recorded once every minute on a data card installed in the MFD.  This data can be downloaded to a PC through an installed RS232 data port under the co-pilot’s panel or the data storage card can be returned to ARNAV for readout and analysis. Either way Cirrus owners have a new way of monitoring the performance and indication trends of their engine and their airplane.  As we experiment with this capability we will pass along our findings.

Engine Economics

It is interesting to speculate on the economic improvement potential in cost of ownership provided by the Engine Monitoring system. Here are some ideas we think about:

• Best Economy compared to Best Power provides substantial reductions in fuel flow, as shown in Figures 7 and 8. Prior to installation of the Engine Monitor, we were reluctant to lean to Best Economy because only one cylinder is monitored by the Cirrus production installation, and that cylinder might not be the first one reach peak EGT when leaning. In fact, before installation of the engine monitor on N365DP, we would get engine knock and roughness before reaching 50 degree lean of peak; a clear indication that one of the unmonitored cylinders was operating too lean. Now we can operate at Best Economy with precision and confidence.
• There is a reduction in true airspeed experienced when operating at the lower fuel flows associated with Best Economy; usually more than the one-knot difference shown in Figures 7 and 8. In our experience so far, it seems like a 20% reduction in fuel flow was achieved by leaning to Best Economy, which caused about a 5 to 7% reduction in true airspeed; still a substantial net gain in miles per gallon. The change in delivered horsepower from leaning to best economy is not reflected in the POH charts or in the % power indication.
• The range and endurance of the airplane and the corresponding need for fuel stops is enhanced by the ability to operate lean of peak. On our leg from Boeing Field to Napa, CA we operated at Best Economy except for the brief time needed to take the photo in Figure 8. Under the conditions of that day, we encountered strong headwinds, and would have made a fuel stop rather than flown the 5 plus hour leg with IFR reserves at the higher fuel consumption associated with Best Power.
• Data recording may have substantial long-term impact on engine maintenance costs and the opportunity to detect engine deterioration before it has an effect on engine condition. This may have particular potential if ARNAV is able to provide owners with comparisons to fleet data upon analysis of fleet data cards.

Fuel Remaining Considerations

Fuel quantity and fuel remaining indications are commonly used on large aircraft to provide a backup in case of a sensor failure since the two systems use completely different sensors and are based on different calculations.  The differences greatly improve the backup value of the combined system.  At the same time inaccuracies and tolerances in both systems can combine to cause a visible disparity of a few gallons during flight.

When we flew four and five-hour legs after selecting full fuel in the selection page (see figure 3) we consistently arrived with more fuel indicated on the tank gages than calculated by the system on the fuel remaining display. The discrepancy ranged from three to five gallons. Since the fuel gages are intended to have maximum accuracy and readability in level flight near the empty state, it is reasonable to assume they are the more reliable indication of actual fuel remaining when the quantity is low. (We did not perform any tests to confirm this by running a tank dry.)

The primary variables affecting the fuel remaining calculation are the total fuel loaded in the tanks and the calibration of the fuel flow sensor.  The primary variables affecting the fuel quantity indication are the actual capacity and shape of the tank and the attitude of the aircraft. Fuel density effects may not match exactly but should be in the same direction for both systems.

There is no precise indication in the tank that shows when it is full. The tab provides a calibration point for partial fueling but full is left to the discretion of the fueler and the pilot. We suspect that fueling differences can be as much as 1 to 3 gallons per tank. Our conclusion is that N365DP with tanks filled to the base of the filler neck holds 60 to 62 usable gallons. It may be that we are fueling into the tank expansion space, or the tanks on our airplane are slightly larger than specified. The result is conservative and tends to increase the range of the airplane at the expense of slightly higher fuel aboard at takeoff.

Summary

The capabilities of the ARNAV MFD Engine Monitoring system are truly impressive and will make engine operation easier for power setting, leaning, monitoring and fuel management. The display window locations keep the pilots’ eyes close to the glare shield where frequent traffic scans are possible during engine operation, system checks, leaning and monitoring. The % Power indication is a great aid to rapid power setting compared to the attention needed to refer to instruments on the far right hand instrument panel and a POH in the pilot’s lap. Leaning the engine by reference to the new vertical indicators is more rapid and precise than using the single EGT gage on the far right of the instrument panel. Thus, he system produces an ability to keep an eye outside the airplane more of the time; an aid to the “see and be seen” method of traffic surveillance. Overall, we really value the reduction in workload and paperwork distractions provided by the engine monitoring displays.

The photos in this article reflect a pre-production version of the Data Acquisition Unit software. ARNAV will be updating their web site to reflect the production and retrofit configuration of the displays. The system is listed as “EngineView” on their web site. We understand that some of the enhancements not connected to engine monitoring are available as a separate upgrade to the ICDS 1000 installation on the Cirrus.

Next steps for new factory airplane installation of the Engine Monitor involve ARNAV acquiring a Supplemental Type Certificate for the system, for which N365DP will be made available. Retrofit of existing airplanes can be accomplished through a FAA Form 337 Field Approval process.

Peter Morton and Delmar Fadden